Antimicrobial isoflavans and other metabolites of Dalea nana

The phytochemical investigation of extracts from Dalea nana roots and aerial parts led to the isolation of thirteen phenolic compounds. Three previously undescribed isoflavans, named verdeans A-C (1, 3, and 7), were characterized. Two additional isoflavans (2 and 5) were previously undescribed enantiomers of known compounds. A previously undescribed isoflavone (verdean D, 10) was found, and the known specialized metabolites, isoflavans 4, 6, 8, and 9, isoflavone 11, flavone 12, and a 2-arylbenzofuran 13, were also isolated. All but one (7) of the isoflavans were prenylated. The structures of the previously undescribed compounds were deduced by NMR spectroscopy, supported by HRESI mass spectrometry. The absolute configurations of 1-3, 5, and 7-9 were determined by ECD. Compounds 1, 3, 4, 6, and 8 exhibited in vitro antimicrobial activities, causing complete growth inhibition (MIC) at concentrations between 6.7 and 37.0 μM against Cryptococcus neoformans and between 8.9 and 25.0 μM against methicillin resistant Staphylococcus aureus (MRSA). The most broadly active previously undescribed compound was verdean A (1), with MIC values of 6.7 and 12.9 μM toward C. neoformans and MRSA, respectively, and an MIC of 10.0 μM against the often-intractable C. albicans.

Antimicrobial Isoflavans and Other Metabolites of Dalea jamesii

The phytochemical investigation of extracts of Dalea jamesii root and aerial portions led to the isolation of ten phenolic compounds. Six previously undescribed prenylated isoflavans, summarily named ormegans A - F (1 - 6: ), were characterized, along with two new arylbenzofurans (7, 8: ), a known flavone (9: ), and a known chroman (10: ). The structures of the new compounds were deduced by NMR spectroscopy, supported by HRESI mass spectrometry. The absolute configurations of 1 - 6: were determined by circular dichroism spectroscopy. Compounds 1 - 9: exhibited in vitro antimicrobial activities, causing 98% or greater growth inhibition at concentrations as low as 2.5 - 5.1 µM against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and Cryptococcus neoformans. Interestingly, the most active compound was the dimeric arylbenzofuran 8: (> 90% growth inhibition at 2.5 µM) against both methicillin-resistant S. aureus and vancomycin-resistant E. faecalis, tenfold more active than its corresponding monomer (7: ).

Absolute configuration of naturally occurring glabridin

The title compound {systematic name: 4-[(3R)-8,8-dimethyl-3,4-dihydro-2H-pyrano[2,3-f]chromen-3-yl]benzene-1,3-diol, commonly named glabridin}, C20H20O4, is a species-specific biomarker from the roots Glycyrrhiza glabra L. (European licorice, Fabaceae). In the present study, this prenylated isoflavan has been purified from an enriched CHCl3 fraction of the extract of the root, using three steps of medium-pressure liquid chromatography (MPLC) by employing HW-40F, Sephadex LH-20 and LiChroCN as adsorbents. Pure glabridin was crystallized from an MeOH-H2O mixture (95:5 v/v) to yield colorless crystals containing one molecule per asymmetric unit (Z' = 1) in the space group P212121. Although the crystal structure has been reported before, the determination of the absolute configuration remained uncertain. Stereochemical analysis, including circular dichroism, NMR data and an X-ray diffraction data set with Bijvoet differences, confirms that glabridin, purified from its natural source, is found only in a C3 R configuration. These results can therefore be used as a reference for the assignment of the configuration and enantiopurity of any isolated or synthetic glabridin sample.

Sphenostylisins A-K: bioactive modified isoflavonoid constituents of the root bark of Sphenostylis marginata ssp. erecta

Sphenostylisins A-C (1-3), three complex dimeric compounds representing two novel carbon skeletons, along with an additional eight new compounds, sphenostylisins D-K (4-11), were isolated from the active chloroform-soluble extract of the root bark of Sphenostylis marginata ssp. erecta using a bioactivity-guided isolation approach. The structures were elucidated by means of detailed spectroscopic analysis, including NMR and HRESIMS analysis, and tandem MS fragmentation was utilized to further support the structures of 1-3. The absolute configuration of sphenostylisin C (3) was established by electronic circular dichroism analysis. Plausible biogenetic relationships between the modified isoflavonoids 1-11 are proposed, and a cyclization reaction of 9 was conducted to support one of the biogenetic proposals made. All of these pure isolates were evaluated against a panel of in vitro bioassays, and among the results obtained, sphenostylisin A (1) was found to be a very potent NF-κB inhibitor (IC50 = 6 nM).

Fungal ABC transporter-associated activity of isoflavonoids from the root extract of Dalea formosa

New potential treatments for disseminated fungal infections are needed, especially for infections caused by the commonly drug-resistant pathogens Candida albicans and C. glabrata. These pathogens cause systemic candidiasis, a significant cause of mortality in immune-compromised patients. ABC transporters of the pleiotropic drug resistance subfamily, such as Cdr1p of C. albicans, play an important role in antifungal resistance and are potential bioassay targets for antifungal therapies against drug-resistant pathogens. We observed strong antifungal growth inhibitory activity in the methanol extract of Dalea formosa roots. This extract afforded six new isoflavonoids, sedonans A-F (1-6), a new but-2-enolide, 4'-O-methylpuerol A (7), and the new pterocarpan ent-sandwicensin (8). The structures and absolute configurations of these compounds were assigned using spectroscopic and chiroptical techniques. The direct antifungal activity of 1 against C. glabrata (MIC = 20 μM) was higher than that of fluconazole. Sedonans A-F and ent-sandwicensin were also active against Saccharomyces cerevisiae strains that express differing ABC transporter-associated resistance mechanisms but differed in their susceptibility to Cdr1p-mediated detoxification. A sedonan A (1)/ent-sandwicensin (8) combination exhibited synergistic growth inhibition. The results demonstrate that multiple crude extract compounds are differentially affected by efflux-mediated resistance and are collectively responsible for the observed bioactivity.

Glabridin

In the title compound, C₂₀H₂₀O₄ {systematic name: 4-[(3R)-8,8-dimethyl-3,4-dihydro-2H-pyrano[2,3-f]chromen-3-yl]benz­ene-1,3-diol}, the hydro­pyran ring linked to the pendant benzene ring adopts an envelope conformation, with the methyne C atom forming the flap. In the crystal, the –OH group at the 3-position of the benzene ring forms an O—H⋯O hydrogen bond to a chromene O-atom acceptor, whereas the –OH group at the 1-position forms an O—H⋯π inter­action with a neighboring benzene ring. The O—H⋯O hydrogen bonds form [001] chains and the O—H⋯π bonds cross-link the chains into (101) sheets. The absolute structure was assumed to be the same as that deduced from previous studies for the natural product.

Amino acid substitutions in naphthalene dioxygenase from Pseudomonas sp. strain NCIB 9816-4 result in regio- and stereo-specific hydroxylation of flavanone and isoflavanone

Wild-type naphthalene dioxygenase (NDO) from Pseudomonas sp. strain NCIB 9816-4 transforms relatively planar flavone and isoflavone to cis-dihydrodiols. However, this enzyme cannot catalyze the transformation of flavanone and isoflavanone in which a phenyl group bonds to the stereogenic C2 or C3 of the C-ring. Protein modeling suggested that Phe224 in the substrate binding site of NDO may play a key role in substrate specificity toward flavanone and isoflavanone. Site-directed mutants of NDO with substitution of Phe224 with Tyr biotransformed only the (S)-stereoisomers of flavanone and isoflavanone, producing an 8-OH group on the A-ring. In contrast, the Phe224Cys and Phe224Gln substitutions, which used (2S)-flavanone as a substrate, and Phe224Lys, which transformed (2S)-flavanone and (3S)-isoflavanone, each showed lower activity than the Phe224Tyr substitution. The remainder of the tested mutants had no activity with flavanone and isoflavanone. Protein docking studies of flavanone and isoflavanone to the modeled mutant enzyme structures revealed that an expanded substrate binding site, due to mutation at 224, as well as appropriate hydrophobic interaction with the residue at 224, are critical for successful binding of the substrates. Results of this study also suggested that in addition to the previously known Phe352, the Phe224 site of NDO appears to be important site for expanding the substrate range of NDO and bringing regiospecific and stereospecific hydroxylation reactions to C8 of the flavanone and isoflavanone A-rings.

Time-dependent density functional theory-assisted absolute configuration determination of cis-dihydrodiol metabolite produced from isoflavone by biphenyl dioxygenase

Escherichia coli cells containing the biphenyl dioxygenase genes bphA1A2A3A4 from Pseudomonas pseudoalcaligenes KF707 were found to biotransform isoflavone and produced a metabolite that was not found in a control experiment. Liquid chromatography/mass spectrometry (LC/MS) and (1)H and (13)C nuclear magnetic resonance (NMR) analyses indicated that biphenyl dioxygenase induced 2',3'-cis-dihydroxylation of the B-ring of isoflavone. In a previous report, the same enzyme showed dioxygenase activity toward flavone, producing flavone 2',3'-cis-dihydrodiol. Due to growing interest in flavone chemistry and the absolute configuration of natural products, time-dependent density functional theory (TD-DFT) calculations were combined with circular dichroism (CD) spectroscopy to determine the absolute configuration of the isoflavone dihydrodiol. By computational methods, the structure of the isoflavone metabolite was determined to be 3-[(5S,6R)-5,6-dihydroxycyclohexa-1,3-dienyl]-4H-chromen-4-one. This structure was confirmed further by the modified Mosher's method. The same protocol was applied to the flavone metabolite, and the absolute configuration was determined to be 2-[(5S,6R)-5,6-dihydroxycyclohexa-1,3-dienyl]-4H-chromen-4-one. After determination of the absolute configurations of the biotransformation products, we suggest the binding mode of these substrate analogs to the enzyme active site.